1. Field of the Invention
The present invention relates to a waste heat recovering apparatus for an engine and particularly to an engine waste heat recovering apparatus arranged for use as a power source in such as a cogeneration system.
2. Description of the Related Art
In view of promotion of the global environmental protection, cogeneration systems have been focused which recovers (exhaust) heat generated by the operation of a heat source and utilizes its energy. For example, a cogeneration system has a gas engine which is provided as the power source and fueled with city gas for generation of electricity and supply of hot water. The cogeneration system also has a waste heat recovering apparatus arranged in which a heat transfer medium such as water is circulated by the action of a water pump through a water jacket for cooling the engine and an exhaust gas heat exchanger for recovering heat from the exhaust gas of the gas engine. More specifically, thermal energy (output) can be produced by transferring the heat from the heat transfer medium which has been heated up by the exhaust gas.
However, if the waste heat recovering apparatus fails to feed its heat transfer medium circulation conduit with a proper amount of the heat transfer medium, the temperature may soar at the heat source or engine and its adjacent area thus creating defectives of the component next to the engine. For instance, shortage of the heat transfer medium is caused by improper replenishment at the maintenance or initial setting, leakage due to the occurrence of failure, or mixture of the air. A modification of the waste heat recovering apparatus is known where an engine protecting circuit is actuated when the temperature of the cooling water rises up to an upper limit level. Such a modification is disclosed in Japanese Patent Laid-open Publication (Heisei)7-247834 where the cooling water fed into the engine cooling section is controlled to stay in a predetermined range of the temperature and minimize the actuation of the engine protecting circuit.
The conventional waste heat recovering apparatus equipped with the engine protecting circuit has a sensor which is provided adjacent to the heat source in the circulation conduit of the cooling water and also used for detecting the occurrence of a fault when its measured temperature exceeds a predetermined threshold level. However, as there is a time lag from the actual increase in the temperature to the measurement of the increased temperature by the sensor, the action of thermal protection may hardly be adequate. It is also necessary to set the predetermined threshold temperature for detecting the occurrence of a fault to a level higher than the upper limit of the heat transfer medium.
An object of the present invention is to provide a waste heat recovering apparatus for an engine which can detect the circulation of an insufficient amount of the heat transfer medium at the earliest possible time to ensure the protection of any heat exposed component.
As a first feature of the present invention, a waste heat recovering apparatus for recovering the waste heat of an engine by circulating a liquid heat transfer medium through a water jacket to cool the engine is provided comprising: a first temperature sensor provided at a waste heat recovering location across the circulation path of the heat transfer medium; a second temperature sensor provided at a downstream of the first temperature sensor across the circulation path; and a means for providing a heat transfer medium shortage signal when a difference in the temperature measurement between the first temperature sensor and the second temperature sensor is greater than a predetermined reference level. As a second feature of the present invention, the waste heat recovering apparatus may be modified in which the heat transfer medium is further conveyed to an exhaust gas heat exchanger which receives heat from the exhaust gas of the engine.
The first and second features allow the heat to be conducted through the air between the first sensor and the second sensor when the heat transfer medium is absent in the circulation path. Accordingly, the difference in the temperature measurement between the two temperature sensors will be greater than that with a sufficient amount of the heat transfer medium circulated in the circulation path. As a result, absence or shortage of the heat transfer medium can favorably be detected by examining whether or not the difference in the temperature measurement exceeds the reference level.
As third feature of the present invention, the waste heat recovering apparatus may be modified in which at least either the first temperature sensor or the second temperature sensor is placed at a location where the air easily stands still in the circulation path. Even if the shortage of the heat transfer medium is small, a mass of the air having a small level of the thermal conductivity is developed between the two temperature sensors because one of the two sensors is located where the air easily stands still. Accordingly, the shortage of the heat transfer medium under progression can be detected at its early stage from the difference in the temperature measurement between the two temperature sensors.
As a fourth feature of the present invention, the waste heat recovering apparatus may be modified in which the first and second temperature sensors are a couple of temperature sensors provided in a fail-safe system. The fourth feature allows the two temperature sensors provide for the fail-safe function to serve as the first and second temperature sensors. Accordingly, the presence, absence, or shortage of the heat transfer medium can favorably be detected with no use of extra sensors.